The dependence of taste buds on the nerve fibers that innervate them has been used as a model to understand nerve/target interactions. Loss of innervation results in a loss of the normal morphological appearance of taste buds, while restoration of innervation results in a restoration of taste bud morphology and function. Therefore, the degenerating and regenerating peripheral gustatory system is ideal for studying dynamic biological processes in which progenitor cells ultimately form mature, functional cells capable of transducing taste information. Previous work in the laboratory of the Principal investigator showed that the adult regenerating gustatory system is especially susceptible to environmental manipulations. Combining unilateral chorda tympani nerve section and low sodium diet in adult rats results in a variety of functional and anatomical alterations in both taste buds and in the regenerating nerve. Furthermore, the effects are not limited to the sectioned side of the tongue because profound functional and anatomical alterations also occur in the intact, contralateral side. To extend these findings, neurophysiological taste responses from single geniculate ganglion cells will be recorded during manipulation of voltages across the lingual epithelium in vivo in control rats and in rats fed either a NaCl-replete or NaCl-deficient diet after unilateral sectioning of the chorda tympani nerve at adulthood. Coordinated morphological studies will examine a variety of processes involved with maintenance and regeneration of receptor cells and associated neural elements. Finally, the role of neural activity and of the immune system will be explored to further an understanding of possible underlying mechanisms involved in the degenerating/regenerating peripheral taste system. The proposed studies will provide new information about: 1) the nature of neurophysiological changes, the site of response alterations, and biophysical changes in the transducing elements in taste receptor cells as a result of nerve sectioning coupled with dietary sodium restriction, 2) the role of the immune system and neural activity in mediating physiological effects, 3) the effects of time, dennervation, and dietary sodium restriction on the stability and accuracy of chorda tympani innervation patterns in single fungiform papillae, and 4) section-induced changes in the numbers of geniculate ganglion cells and chorda tympani fibers. Findings from these studies will provide further information about the plasticity of peripheral taste responses and the neuroanatomical organization in the normal and regenerating adult peripheral gustatory system. They will also be useful in determining the role that diet has on regenerating nerves and on sensory receptor function and anatomy.